Snowmobiles typically include a frame having a front portion for mounting the engine and the front suspension and a rear portion consisting of a tunnel conventionally made of sheet metal to accommodate and cover the drive track and rear suspension of the snowmobile underneath and to support the straddle seat of the snowmobile above. Snowmobile tunnels conventionally have a square c-shape profile which means that the side walls of the tunnel are generally perpendicular to the top portion of the tunnel. The side walls of the tunnel typically extend downwardly from the top portion of the tunnel in a generally orthogonal manner. The side walls of the tunnel are spaced apart to receive the drive track therebetween and are provided with mounting points for the rear suspension. A pair of footrests is typically mounted to the outer portion of each side wall to help position and support the rider in a comfortable posture while providing adequate ground clearance for the snowmobile.
FIG. 1 is a rear cut-away view of a conventional snowmobile in which the tunnel 12 has a square c-shape profile defined by the top portion 12a and the sidewalls 12b. The upper portion of the drive track 16 is accommodated within the tunnel 12 and the rear suspension assembly 18 is mounted to a transverse shaft 20 itself mounted to the sidewalls 12b. A pair of footrests 26 is mounted to the outer side of each side wall 12b. A straddle seat 14 comprising a rigid supporting framework 22 is mounted onto the tunnel 12 and the width T1 of the tunnel 12 generally dictates the minimum width S1 of the straddle seat 14.
When a rider is cornering aggressively, he leans his body weight towards the inside of the corner to affect the center of gravity of the snowmobile in such a way that his body is positioned on the inner side of the straddle seat, his inside upper leg resting on the straddle seat with the lower leg holding on to the side of the straddle seat. In a conventional snowmobile design as depicted in FIG. 1, the edge 24 of the straddle seat 14 may press into the leg of the rider causing discomfort and rendering the aggressive driving experience less pleasant.
For snowmobiles having wide tracks, the problem is exacerbated since the tunnel 12 has to be wider to accommodate wider track 16 and the straddle seat 14 is typically at least as wide as the tunnel 12. With a wider straddle seat 14, the edge 24 of the straddle seat 14 will be in contact with the leg of the rider as soon as the rider begins to lean into the corners and it may even be difficult to lean into a corner without having to lift one's foot off the outside footrest 26. Furthermore, the wider seat 14 associated with a wide track may even be uncomfortable for a shorter person to straddle as his or her legs must be spread at least as wide as the straddle seat.
One solution to the problem associated with extra-wide seats has been to place a standard-size seat, i.e. a seat designed for a standard 15-inch tunnel, on a tunnel that is designed for a 20- or 24-inch wide track. However, this solution exposes the wide tunnel structure and the edges of the wide tunnel which end up being directly in contact with the rider's legs and this contact tends to transfer the normal vibrations of the snowmobile directly to the rider. Furthermore, the edges of the wide tunnel having a typical square profile tend to press into the rider's legs during aggressive cornering, causing discomfort.
Thus, there is a need for a snowmobile having a tunnel design that alleviates some of the problems related to conventional tunnel design and improves the comfort of the rider in various manoeuvring.